From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tetsuya Mukawa <mukawa@igel.co.jp>
Subject: Re: [PATCH v5 2/3] vhost: Add VHOST PMD
Date: Fri, 18 Dec 2015 18:25:47 +0900
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Cc: dev@dpdk.org, ann.zhuangyanying@huawei.com, yuanhan.liu@intel.com
To: Yuanhan Liu <yuanhan.liu@linux.intel.com>,
 "Xie, Huawei" <huawei.xie@intel.com>
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On 2015/12/18 16:45, Yuanhan Liu wrote:
> On Tue, Nov 24, 2015 at 06:00:02PM +0900, Tetsuya Mukawa wrote:
>> +static uint16_t
>> +eth_vhost_rx(void *q, struct rte_mbuf **bufs, uint16_t nb_bufs)
>> +{
>> +	struct vhost_queue *r = q;
>> +	uint16_t i, nb_rx = 0;
>> +
>> +	if (unlikely(rte_atomic32_read(&r->allow_queuing) == 0))
>> +		return 0;
>> +
>> +	rte_atomic32_set(&r->while_queuing, 1);
>> +
>> +	if (unlikely(rte_atomic32_read(&r->allow_queuing) == 0))
>> +		goto out;
> I'm not quite famililar with PMD driver yet, but as far as I know,
> rte_eth_rx/tx_burst() does not provide any garantee on concurrent
> dequeuing/queuing. If that's true, vhost pmd could (and should)
> not do that, to keep the consistency.

Yes you are correct, but this checking isn't for that purpose.
I guess there is no rule that DPDK application should not call
rte_eth_rx/tx_burst() when link status is down.
So the application may call rte_eth_rx/tx_burst() even when vhost
backend connection isn't established.
Not to call rte_vhost_dequeue_burst() in the case, above variables are used.

Tetsuya

> On the other hand, rte_vhost_dequeue/enqueue_burst() already has
> such support since the beginning: above check is redundant then.
> However, FYI, Huawei has just (internally) proposed to remove
> it, as he thinks that's application's duty.
>
> So, in neither way, we should not do that.
>
> 	--yliu